That sounds a huge drop.
Entirely possible, but its unlikely to stay off and your immune system will suffer.
Long term or permanent weight loss are gradual processes which rely primarily on nutrition, with exercise supporting the weight loss.

In order to shed actual fat (as opposed to just water...) one of the best methods is a treadmill - 8kmph with a gradient of say 15%
Utilise this for 40mins - 1hr and it will attack the fat.